An experimental program is developed to investigate the three dimensional nature of the stress field surrounding the border of semi-elliptical surface flaws, particularly the singularity exponent. Stress freezing photoelasticity is employed to generate experimental data from nearly incompressible, elastic material. The technique of optical fringe multiplication is utilized to collect data from thin, closely spaced photoelastic slices.

A new quasi-linear algorithm for data analysis is developed and verified. The algorithm is implemented using the interactive and graphics capabilities of a microcomputer and digitizing tablet, saving time and reducing errors in photoelastic data analysis. By utilizing CRT graphics, the measurement zone producing the most consistent results is delineated.

Results obtained from a series of tests on both surface flaws and straight-front cracks bracket analytical values of the singularity exponent at the flaw border-free surface intersection. Suggestions to decrease variance in the results and possibly cause the results for all tests to coalesce to the analytical value(s) at the free surface are presented.

An algebraic formula is developed to account for the singularity exponent variation (3-D effect) by adjusting the magnitude of the classical LEFM mode I stress intensity factor, K_I. A discussion of the need to recognize and account for these effects in high-tech materials is also included.